Systems and methods for measuring electrical characteristic of medical fluids

ABSTRACT

A device for measuring conductivity of a fluid. The device including a chamber and at least two electrodes. The chamber includes an inlet, an outlet, an upper surface, and a lower surface that runs separate from the upper surface. The fluid enters the chamber through the inlet and flows out of the chamber through the outlet. Moving along a length of the chamber from the inlet to the outlet or from the outlet to the inlet, a distance between the upper surface and the lower surface changes in at least one dimension of the chamber. The two electrodes are configured to measure electrical voltage in the fluid that enters the chamber through the inlet and flows out of the chamber through the outlet.

CLAIM OF PRIORITY

This application claims priority under 35 USC § 119(e) to U.S. PatentApplication Ser. No. 62/860,046, filed on Jun. 11, 2019, the entirecontents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to measuring conductivity of a medical fluid.

BACKGROUND

During hemodialysis, impurities and toxins are removed from the blood ofa patient by drawing the blood out of the patient through a blood accesssite, typically via a catheter, and then passing the blood through anartificial kidney (often referred to as a “dialyzer”). The artificialkidney includes a semi-permeable membrane that separates a first conduitfrom a second conduit. Generally, a dialysis solution (often referred toas a “dialysate”) flows through the first conduit of the dialyzer whilethe patient's blood flows through the second conduit of the dialyzer,causing impurities and toxins to be transferred from the blood to thedialysate through the semi-permeable membrane. The impurities and toxinscan, for example, be removed from the blood by a diffusion process.After passing through the dialyzer, the purified blood is then returnedto the patient.

Maintaining a substantially constant concentration of sodium in thepatient's blood throughout the hemodialysis treatment can help to reduceor prevent discomfort experienced by the patient. Therefore, sodiumconcentrations in the patient's blood and in the dialysate can bemonitored during hemodialysis treatment.

SUMMARY

Implementations of the present disclosure are directed to a disposabledevice for measuring electrical characteristics of medical fluids, suchas blood in dialysis systems. The device has a configuration thatdirects bubbles in the fluid away from electrodes that measure theelectrical characteristics of the fluid.

In some implementations, the disposable device that includes a chamberand two electrodes. The chamber including an inlet, an outlet, an uppersurface, and a lower surface that runs separate from the upper surface.The fluid enters the chamber through the inlet and flows out of thechamber through the outlet. Moving along a length of the chamber fromthe inlet to the outlet or from the outlet to the inlet, a distancebetween the upper surface and the lower surface changes in at least onedimension of the chamber. The two electrodes are configured to measureelectrical voltage in the fluid that enters the chamber through theinlet and flows out of the chamber through the outlet. Otherimplementations include corresponding methods and systems configured toperform the actions needed to measure electrical characteristics offluid.

In some embodiments, the chamber is disposable and is calibrated for aspecific cell constant that is determined based on location of the twoelectrodes with respect to each other. In some examples, conductivity ofthe fluid is determined by dividing the constant cell to an impedance ofthe fluid, the impedance being determined based on the measuredelectrical voltage.

Some embodiments include an air detector sensors configured to detectthat at least one of the two electrodes is exposed to air. The airdetector sensor can include at least two sensor electrodes, each sensorelectrode including having a respective conductive tip configured toreceive or transmit an electrical current when sunk in a non-gaseousenvironment.

In some embodiments, the upper surface is in a concave shape. In someembodiments, the chamber has a curved side wall that connects the uppersurface to the lower surface. The side wall may form an elliptical crosssection for the chamber. In some embodiments, the length of the chamberis less than 5 centimeters.

Some embodiments include two additional electrodes, wherein the twoelectrodes measure the electrical voltage when the two additionalelectrodes apply the electrical current to the fluid.

The inlet can be connected to a peristaltic pump configured to pump thefluid into the chamber.

The device is attachable to a dialysis system. For example, the chambermay be formed in a cassette that is insertable into the dialysis system.The dialysis system can be a hemodialysis system or can include aperitoneal dialysis machine.

The present disclosure also describes methods of measuring conductivityof a fluid. One method includes receiving, through an inlet of achamber, the fluid, wherein the fluid flows within the chamber and aboutmultiple electrodes located in the chamber; applying an electricalcurrent to first two electrodes of the multiple electrodes; measuring anelectrical voltage between second two electrodes of the multipleelectrodes; and measuring electrical conductivity of the fluid based onthe applied electrical current and the measured electrical voltage,wherein the chamber is designed so that bubbles within the fluid aredirected away from the electrodes.

This and other methods described herein can optionally include one ormore of the following actions: the method includes pumping the fluid outof the chamber by applying pressure pulses to the fluid; the methodincludes detecting, by at least two air detector sensors, that at leasta tip of at least one electrode is exposed to air; each of the airdetector sensors has a height that is equal or larger than a height ofthe at least one electrode, the heights being measured in a directionperpendicular to a bottom surface of the chamber; the fluid comprises amedical fluid or blood; the chamber has an upper surface, and a lowersurface that runs separate from the upper surface, and moving along alength of the chamber from the inlet to the outlet or from the outlet tothe inlet, a distance between the upper surface and the lower surfacechanges in at least one dimension of the chamber.

Devices and methods in accordance with the present disclosure mayinclude any combination of the aspects and features described herein.That is, devices in accordance with the present disclosure are notlimited to the combinations of aspects and features specificallydescribed herein, but also include any combination of the aspects andfeatures provided.

Implementations of the present disclosure provide one or more of thefollowing technical advantages and/or technical improvements overpreviously available solutions. The implementations allow monitoringfluid parameters (e.g., concentration, fluid elements, etc.) of amedical fluid by measuring electrical characteristics of the fluid. Forexample, a dialysate should have a conductivity that indicates that acertain amount and ratio of sodium bicarbonate is present, because animbalance could impact the health of the patient and cause discomfort.The present implementations provide a contactless sensor that canmeasure conductivity of the dialysate without making direct contact(e.g., via electrodes) with the patient's body.

The implementations include a pre-calibrated and disposable datacollecting cell that collects data of the fluid's electricalcharacteristics (e.g., electrical voltage). The pre-calibrated celleliminates a need to calibrate the cell for each use, which makes iteasier for an unsophisticated patient to use the cell at home andwithout assistance of a medical staff. For example, a patient may insertor attach the cell to a dialysis system to monitor their bloodparameters and adjust the dialysis system accordingly without beingworried about calibrating the cell before use. In addition, the cell canbe very light weighted and substantially small, which makes it easy tocarry, store, and use. Further, the cell is designed to improve accuracyin measuring the fluid's electrical characteristics by directing gas(e.g., air) bubbles away from the cell's electrodes.

The details of one or more implementations of the present disclosure areset forth in the accompanying drawings and the description below. Otherfeatures and advantages of the present disclosure will be apparent fromthe description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 depicts an example application of the implementations of thepresent disclosure.

FIG. 2 illustrates an example of a peritoneal dialysis (PD) system.

FIG. 3A illustrates a perspective views an example data collecting cellaccording to implementations of the present disclosure.

FIG. 3B illustrates a bottom view of the data collecting cell of FIG.3A.

FIG. 4 illustrates fluid flow in an example data collecting cellaccording to implementations of the present disclosure.

FIG. 5 illustrates an example data collecting cell including a gasdetector sensor according to implementations of the present disclosure.

FIG. 6 depicts an example process that can be executed in accordancewith the implementations of the present disclosure.

FIG. 7 shows an example of a computer system and related components.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Implementations of the present disclosure provide a device that can beused to measure one or more electrical characteristics (e.g., electricalconductivity) of fluids such as blood in dialysis systems. The devicehas a disposable data collecting cell that can be replaced after acertain number of uses, for example, after every use. The cell includesa chamber with an inlet and an outlet. Fluid enters the chamber throughthe inlet and flows out of the chamber through the outlet. Multipleelectrodes are located within the chamber to measure electricalcharacteristics of the fluid.

The chamber is designed to direct bubbles within the fluid away from theelectrodes. In some implementations, moving along the length of thechamber from the inlet to the outlet, a distance between an uppersurface and a lower surface of the chamber varies so that the bubbleswould be directed from the lower distance region to the higher distanceregion. The electrodes can be located at the lower distance region ofthe chamber. For example, the upper surface of the chamber can be inconcave shape and the electrodes can be located away from edges of theconcaved upper surface to which the bubbles are directed.

FIG. 1 depicts an example application of the implementations of thepresent disclosure. As depicted, a system 100 is connected to a patient102. The system 100 can include a dialysis system (e.g., a peritonealdialysis machine) to dialyze the patient's blood. The system 100includes a data collecting unit 104, and a measurement unit 106.

Patient's blood flows from the patient 102's body to the data collectingunit 104 through a first conduit 108, and flows back from the datacollecting unit 104 to the patient's body through a second conduit 110.During this process, the data collecting unit 104 collects data of thepatient's blood. Data collected by the data collecting unit 104 istransferred to the measurement unit 106 through the communicationchannel 112. The communication channel can be a wired and/or a wirelesschannel.

The measurement unit 106 includes one or more devices to measureelectrical characteristic(s) of the blood based on the data receivedfrom the data collecting unit 104. For example, the measurement unit 106can include an impedance analyzer to measure impedance or conductivityof the blood. The measurement unit 106 can also include one or morepower supplies that generate an electrical current, which is transmittedthrough the communication channel 112 to the data collecting unit 104 toexcite the blood.

FIG. 2 shows an example of the system 100 of FIG. 1 . In particular,FIG. 2 shows an example peritoneal dialysis system 200 that can mayinclude the data collecting unit 104 and the measurement unit 106described above. The peritoneal dialysis system 200 includes a PDmachine (also generally referred to as a PD cycler) 202 seated on a cart204. The PD machine 202 includes a housing 206, a door 208, and acassette interface 210 that contacts a disposable PD cassette 212 whenthe cassette 212 is disposed within a cassette compartment 214 formedbetween the cassette interface 210 and the closed door 208. A heatertray 216 is positioned on top of the housing 206. The heater tray 216 issized and shaped to accommodate a bag of PD solution such as dialysate(e.g., a 5 liter bag of dialysate). The PD machine 202 also includes auser interface such as a touch screen display 218 and additional controlbuttons 220 that can be operated by a user (e.g., a caregiver or apatient) to allow, for example, set up, initiation, and/or terminationof a PD treatment.

Dialysate bags 222 are suspended from fingers on the sides of the cart204, and a heater bag 224 is positioned in the heater tray 216. Thedialysate bags 222 and the heater bag 224 are connected to the cassette212 via dialysate bag lines 226 and a heater bag line 228, respectively.The dialysate bag lines 226 can be used to pass dialysate from dialysatebags 222 to the cassette 212 during use, and the heater bag line 228 canbe used to pass dialysate back and forth between the cassette 212 andthe heater bag 224 during use. In addition, a patient line 230 and adrain line 232 are connected to the cassette 212. The patient line 230can be connected to a patient's abdomen via a catheter and can be usedto pass dialysate back and forth between the cassette 212 and thepatient's peritoneal cavity during use. The catheter may be connected tothe patient line 230 via a port such as a fitting. The drain line 232can be connected to a drain or drain receptacle and can be used to passdialysate from the cassette 212 to the drain or drain receptacle duringuse.

The PD machine 202 also includes a control unit 239 (e.g., a processor).The control unit 239 can receive signals from and transmit signals tothe touch screen display 218, the control panel 220, and the variousother components of the PD system 200. The control unit 239 can controlthe operating parameters of the PD machine 102. In some implementations,the control unit 239 is an MPC823 PowerPC device manufactured byMotorola, Inc.

Referring back to FIG. 1 , the data collecting unit 104 includes a datacollecting cell that has multiple electrodes to electrically excite theblood and to measure electrical voltage within the blood. FIG. 3Aillustrates a perspective view of an example data collecting cell 300.The cell 300 includes a chamber 302 with an inlet 308 and an outlet 310.Fluid (e.g., blood, medical fluids) enters the chamber 302 through theinlet 308 and flows out of the chamber through the outlet 310. Multipleelectrodes 304 a, 304 b, 304 c, and 304 d are located within the chamberto measure electrical parameters (such as electrical voltage) of thefluid in response to applying an electrical current to the fluid.

The chamber 302 contains multiple electrodes 304 a, 304 b, 304 c, and304 d. Two or more electrodes are used to apply electrical current tothe fluid, and two or more electrodes are used to measure electricalvoltage. For example, electrodes 304 a and 304 d can be connected to apower supply of the measurement unit 106, and electrodes 304 b and 304 ccan be connected to a measuring device, such as an impedance analyzer,in the measurement unit 106. Alternatively, the same electrodes thatapply current can also measure voltage.

The chamber 302 has an upper surface 312 and a lower surface 314. Movingalong the length of the chamber from the inlet 308 to the outlet 310 (indirection x), the distance between the upper surface 312 and the lowersurface 314 varies. In the illustrated example, the distance between theupper and the lower surfaces is greater at about the inlet and theoutlet regions of the chamber than at the region where the electrodesare located. Such configuration directs the gas bubbles (e.g., airbubbles) in the fluid away from the electrodes and towards the outlet(or towards the inlet depending on the fluid flow's speed).

In the example cell 300, the upper surface of the chamber has a concaveshape, and the distance between the upper and the lower surfaces isminimum at a region halfway between the inlet and the outlet. However,the minimum distance can be at any part of the cell. For example, theminimum distance may be in the first half of the chamber along directionx (i.e., closer to the inlet than to the outlet) or in the second halfof the chamber along direction x (i.e., closer to the outlet than to theinlet).

In the example cell 300, the distance between the upper and the lowersurfaces is greatest close to the inlet and the outlet regions of thechamber. In other embodiments, the greatest distance may be at any partof the chamber, e.g., other than where the electrodes are located. Inother words, the upper surface 212 is not at its greatest distance fromthe lower surface 214 directly above the electrodes (but does not haveto be at its minimum distance directly above the electrodes, either).

The illustrated upper surface 312 of the example cell 300 is curved.Alternatively, the upper surface can be designed as a set of multipleinclined plates. For example, the upper surface can include twodiverging plates that intersect at a common line at a region between theinlet and outlet (along direction x), forming a V-shape upper surface.An upper surface of a cell can have a combination of curved and platesurfaces.

The illustrated upper surface 212 in FIG. 3A is connected to the inletand the outlet by respective connector walls 316. Alternatively, one orboth of the connector walls can be eliminated so that the inlet and/orthe outlet is formed on a portion of the upper surface 312.

The upper surface 312 is connected to the bottom surface 314 throughside walls of the chamber (now shown in FIG. 23A). FIG. 3B illustrates abottom view of the cell 300 that depicts a bottom profile of the sidewalls 320 and 322. As illustrated, the side walls 320 and 322 of thechamber are curved. For example, the chamber 302 can have an ellipticalcross section. Curved side walls help in reducing turbulent fluid flowand provide a laminar fluid flow through the chamber.

FIG. 4 illustrates fluid flow in an elliptical chamber 402. Asillustrated, since the chamber 402 does not have any corners, the fluiddoes not get trapped in any particular part of the chamber, and ratherflows smoothly throughout the chamber.

Referring back to FIG. 3A, the example cell 300 includes fourelectrodes, however, cells with more or less number of electrodes (e.g.,two or three electrodes) can also be designed. For example, a cell canbe designed to have only two electrodes, where the same electrodes applythe electrical current and measure the voltage of the two electrodes.Additional electrodes (e.g., four) can improve measurement accuracy asseparate set of electrodes can be used for applying current andmeasuring voltage. Relatively fewer electrodes (e.g., two) can help inreducing the size of the cell.

Once connected to the power supply, the cell 302 can provide anexcitation electrical current to the fluid. The electrical current canhave a frequency ranging from DC to 100 kHz. The excitation current canbe in any bipolar or unipolar AC form such as sinusoidal, sawtooth,square wave shape, etc.

The excitation current that is being applied to the electrodes can belimited to a predetermined threshold. The threshold can be below 50milliAmpere (mA), e.g., 10 mA. Limiting the current to a low thresholdvalue guaranty safety in handling the device. Further, a chance ofelectrical shortening or damages by the exposed electrode contacts canbe reduced by limiting the current that can pass through the circuitrythat transmits current from the power supply to the cell. For example,the circuitry can have bidirectional diodes that limit the maximumvoltage across different sections of the circuit to a threshold voltage,e.g., 1 volt.

As noted above, the data collecting cell is disposable and can bedetached from system 100 (e.g., a dialysis system, such as the PD system200 of FIG. 2 ) after a certain number of uses (e.g., one-time use). Theeach cell can be pre-calibrated during the manufacturing process beforebeing provided to consumers. This feature provides a consumer-friendlyfeature that allows patients to replace the cell after a certain numberof use without being worried about recalibrating the cell before eachuse.

To eliminate a need to calibrate the data collection cell for each use,each cell can be designed for a specific cell constant. The calibrationcan stay accurate for a predetermined number of use, and the cell can bedisposed afterwards. For example, a cell may be calibrated for 13.8millisiemens (mS) and may be set for one time use. The calibration maybe set for a specific temperature, e.g., 37 Celsius, and/or a specifictype of fluid (e.g., blood, urine, saline, etc.).

A cell constant (that is used to calibrate a cell) is a measurement ofthe fluid volume contained between the two measuring electrodes, forexample, electrodes 304 b and 304 c that measure the electrical voltage.A data collecting cell may be designed for a particular cell constant.Parameters of the measurement unit 106 to which the data collecting cellis to be attached, may determine the particular cell constant. Forexample, the data collecting cell can be designed to have a cellconstant between 12-16 millisiemens (mS), for example, 14 mS.

A cell constant of a data collecting cell depends on the geometry of andthe distance between two measuring electrodes of the cell. Theelectrodes can have any shape. However, electrodes with curved crosssection (e.g., cylindrical electrodes similar to the electrodes depictedin FIGS. 3A and 3B) are preferred to electrodes that have one or morecorners (e.g., cubic or pyramid shaped electrodes) because curvaturereduces fluid turbulence in the chamber as compared to edges.

Electrical conductivity of a fluid in a cell can be calculated based onthe cell constant of the cell using the following formula:

$\begin{matrix}{{{Conductivity} = {\frac{K}{Resistance} = \frac{K}{Z*{\cos(\Phi)}}}},} & {{Equation}\mspace{14mu} 1}\end{matrix}$where K is the cell constant, Z is an impedance (e.g., in ohm) of thefluid, and Φ is phase angle (e.g., in degrees). Conductivity can bemeasured in milliSiemens per centimeter (mS/cm).

In order to get an accurate measurement of the fluid's electricalcharacteristics, at least the measuring electrodes that measureelectrical voltage (or at least the conductive portion of the measuringelectrodes) should be completely immersed/sunk in the fluid. An exposureof a conductive portion of a measuring electrode to air can lead toinaccuracy in measuring electrical characteristics of the fluid.

A data collecting cell can include a gas detector sensor that alerts anexposure of one or more electrodes to air (or to other gasses within thechamber, or to vacuum). FIG. 5 illustrates an example data collectingcell 500 including a gas detector sensor 502 within the cell's chamber.The gas detector sensor 502 includes multiple sensor electrodes 502 aand 502 b. Each sensor electrode is an insulated conductors and has arespective conductive portion. The conductive portions are configured totransmit an electrical current when sunk in a fluid. However, no currentis transmitted between the conductive portions of the two sensorelectrodes when the conductive portions are exposed to a gaseousenvironment such as air. Accordingly, when no current is transmittedbetween the sensor electrodes, the sensor 502 detects that the fluidlevel is too low and at least one of the measuring electrodes is exposedto air.

In the example data collecting cell 500, the conductive portions of thesensor electrodes 502 a and 502 b are at their respective tips 504. Atleast one of the two sensor electrodes 502 a and 502 b can be designedto be taller than at least one of the measuring electrodes (e.g., themeasuring electrode 506) of the cell 500 in order to detect situationswhen the measuring electrode (or a portion of it) is exposed to air. Forexample, in the tilted position illustrated in FIG. 5 , the fluid levelis dropped below the measuring electrode 506's height, causing a portionof the measuring sensor 506 to stick out of the fluid and be exposed toair.

In some embodiments, the sensor electrodes are taller than any of theexcitation electrodes (i.e., electrodes that apply the excitationelectrical current) or measuring electrodes (i.e., electrodes thatmeasure electrical voltage) of the cell. In some embodiments, two ormore sensor electrodes are assigned to particular excitation ormeasuring electrode(s). For example, the electrodes 502 a and 502 b maybe set to detect exposure of electrode 406 to air, irrespective ofwhether or not any other electrode is sunk in the fluid or exposed toair.

Referring back to FIGS. 1 and 3A, the system 100 can also include a pumpconfigured to pressurize the fluid inside the data collecting cell 300of the data collecting unit 104. The pump (not shown) can be attached tothe data collecting unit 104, or either of the first or the secondconduits 108, 110. The pump can be a peristaltic pump that appliespressure pulses to the fluid. Such pulses force gas bubbles that areattached to any part of the data collecting cell (e.g., the electrodes,the side walls, or the lower or upper surfaces of the chamber) to bedetached and be moved towards the outlet. Using peristaltic pumps isparticularly helpful in removing smaller bubbles that may be harder toremove, especially in a constant or low-speed fluid current.

The cell's size and weight are substantially small, which provideconvenient handling and carrying by a single person. For example, thedevice can have dimensions smaller than 5 cm×5 cm×5 cm (e.g., 1 cm×3cm×3 cm), and can be made of plastic.

FIG. 6 depicts an example process 600 that can be executed in accordancewith the implementations of the present disclosure. The process 600 canbe implemented by system 100 (e.g., the PD system 200) including thedata collecting cell 300, or by any other system capable of performingthe process 600.

In this process, fluid is received through an inlet of a chamber andflows about multiple electrodes located within the chamber (602). Forexample, fluid can be received at the chamber 302 through the inlet 308.The fluid passes through the chamber and about the electrodes 304 athrough 304 d. The electrodes can be connected to a measurement unit, apower supply, and/or a dialysis machine.

An electrical current is applied to a first set of electrodes within thechamber (604). For example, the electrodes 304 a and 304 d may transmitelectrical current through the fluid within the chamber. The electrodes304 a and 304 d are connected to a power supply, for example, located inthe measurement unit 106.

Electrical voltage is measured between a second set of electrodes withinthe chamber (606). For example, the electrodes 304 b and 304 c canmeasure the electrical voltage upon the application of an electricalcurrent to the fluid. The second set of electrodes can be the same ordifferent from the first set of electrodes. Having the two sets separatewould improve measurement accuracy but would also increase the chambersize needed for setting the electrodes.

Fluid can be pumped out of the chamber through an outlet of the chamber(608). For example, pressure pulses can be applied to the fluid to pumpthe fluid out of the chamber. Such pressure pulses help in removingsmall bubbles from the fluid.

Conductivity (or any other desired electrical characteristics) of thefluid is measured (or calculated) based on the applied electricalcurrent and the measured electrical voltage (610). For example, theelectrodes that measured the electrical voltage can transmit theirmeasured data to a measurement unit (e.g., an impedance analyzer) tocalculate the conductivity of the current.

The chamber is designed so that bubbles within the fluid are directedaway from the electrodes. For example, the chamber can have a lowersurface, and an upper surface separated from the lower surface. In someimplementations, the lower surface is parallel to a portion of the uppersurfaces in which the inlet and outlet are formed. Moving along a lengthof the chamber from the inlet to the outlet, a distance between theupper surface and the lower surface changes in at least one dimension ofthe chamber (e.g., in a direction perpendicular to the lower surface).The upper surface can be similar to the upper surface 312 in FIG. 3A.

FIG. 7 is a block diagram of an example computer system 700 that can beused as part of the system 100 of FIG. 1 , for example to perform themeasurements or analysis of the measurement unit 106. For example, acontrol unit, a computing device, and/or a microcontroller could beexamples of the system 700 described here. The system 700 includes aprocessor 710, a memory 720, a storage device 730, and an input/outputdevice 740. Each of the components 710, 720, 730, and 740 can beinterconnected, for example, using a system bus 750. The processor 710is capable of processing instructions for execution within the system700. The processor 710 can be a single-threaded processor, amulti-threaded processor, or a quantum computer. The processor 710 iscapable of processing instructions stored in the memory 720 or on thestorage device 730. The processor 710 may execute operations such ascausing the dialysis system to carry out dialysis functions.

The memory 720 stores information within the system 700. In someimplementations, the memory 720 is a computer-readable medium. Thememory 720 can, for example, be a volatile memory unit or a non-volatilememory unit. In some implementations, the memory 720 stores informationfor causing the pumps of the dialysis system to operate as describedherein.

The storage device 730 is capable of providing mass storage for thesystem 700. In some implementations, the storage device 730 is anon-transitory computer-readable medium. The storage device 730 caninclude, for example, a hard disk device, an optical disk device, asolid-date drive, a flash drive, magnetic tape, or some other largecapacity storage device. The storage device 730 may alternatively be acloud storage device, e.g., a logical storage device including multiplephysical storage devices distributed on a network and accessed using anetwork.

The input/output device 740 provides input/output operations for thesystem 700. In some implementations, the input/output device 740includes one or more of network interface devices (e.g., an Ethernetcard), a serial communication device (e.g., an RS-232 10 port), and/or awireless interface device (e.g., an 802.11 card, a 3G wireless modem, ora 4G wireless modem). In some implementations, the input/output device740 may include short-range wireless transmission and receivingcomponents, such as Wi-Fi, Bluetooth, and/or near field communication(NFC) components, among others. In some implementations, theinput/output device includes driver devices configured to receive inputdata and send output data to other input/output devices, e.g., keyboard,printer and display devices (such as the touch screen display 118). Insome implementations, mobile computing devices, mobile communicationdevices, and other devices are used.

In some implementations, the system 700 is a microcontroller. Amicrocontroller is a device that contains multiple elements of acomputer system in a single electronics package. For example, the singleelectronics package could contain the processor 710, the memory 720, thestorage device 730, and input/output devices 740.

The measurement unit and/or the data collection unit described hereincan be part of any medical system, such as dialysis systems (e.g., ahemodialysis system), a heart lung machine, a chemotherapy system, orany other system that introduces fluid into body.

While blood was used herein as an example fluid for describing thefunctionality of the embodiments, the data collecting unit, in general,and the data collecting cell, in particular, can be used for determiningelectrical characteristics of any other type of fluids, or any medicalfluids such as plasma, saline, or urine, to name a few.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A device for measuring conductivity of a fluid,the device comprising: a chamber that includes: an inlet, an outlet,wherein the fluid enters the chamber through the inlet and flows out ofthe chamber through the outlet, an upper surface, and a lower surfacethat runs separate from the upper surface, wherein the upper surface hasat least a concave portion such that moving along a length of thechamber from the inlet to the outlet or from the outlet to the inlet, adistance between the upper surface and the lower surface changes in atleast one dimension of the chamber so that bubbles in the fluid aredirected from a lower distance region to a higher distance region alongthe concave portion of the upper surface and towards the outlet or theinlet; and two electrodes configured to measure electrical voltage inthe fluid that enters the chamber through the inlet and flows out of thechamber through the outlet.
 2. The device of claim 1, wherein thechamber is disposable and is calibrated for a specific cell constantthat is determined based on location of the two electrodes with respectto each other.
 3. The device of claim 2, wherein the conductivity of thefluid is determined by dividing the cell constant to an impedance of thefluid, the impedance being determined based on the measured electricalvoltage.
 4. The device of claim 1, further comprising an air detectorsensor configured to detect that at least one of the two electrodes isexposed to air.
 5. The device of claim 4, wherein the air detectorsensor comprises at least two sensor electrodes, each sensor electrodeincluding a respective conductive tip configured to receive or transmitan electrical current when sunk in a non-gaseous environment.
 6. Thedevice of claim 1, wherein the upper surface is in a concave shape. 7.The device of claim 1, wherein the chamber has a curved side wall thatconnects the upper surface to the lower surface.
 8. The device of claim7, wherein the side wall forms an elliptical cross section for thechamber.
 9. The device of claim 1, further comprising two additionalelectrodes, wherein the two electrodes measure the electrical voltagewhen the two additional electrodes apply an electrical current to thefluid.
 10. The device of claim 1, wherein the inlet is connected to aperistaltic pump configured to pump the fluid into the chamber.
 11. Thedevice of claim 1, wherein the length of the chamber is less than 5centimeters.
 12. The device of claim 1, wherein the device is configuredto be attached to a dialysis system.
 13. The device of claim 12, whereinthe chamber is formed in a cassette that is insertable into the dialysissystem.
 14. The device of claim 12, wherein the dialysis system includesa peritoneal dialysis machine.
 15. A method of measuring conductivity ofa fluid, the method comprising: receiving, through an inlet of achamber, the fluid, wherein the fluid flows within the chamber and aboutmultiple electrodes located in the chamber; applying an electricalcurrent to first two electrodes of the multiple electrodes; measuring anelectrical voltage between second two electrodes of the multipleelectrodes; and measuring electrical conductivity of the fluid based onthe applied electrical current and the measured electrical voltage,wherein the chamber has a surface with at least a concave portion sothat bubbles within the fluid are directed away from the electrodesalong the concave portion and towards the inlet or an outlet of thechamber.
 16. The method of claim 15, further comprising pumping thefluid out of the chamber by applying pressure pulses to the fluid. 17.The method of claim 15, further comprising detecting, by at least twoair detector sensors, that at least a tip of at least one electrode isexposed to air.
 18. The method of claim 17, wherein each of the airdetector sensors has a height that is equal or larger than a height ofthe at least one electrode, the heights being measured in a directionperpendicular to a bottom surface of the chamber.
 19. The method ofclaim 16, wherein the fluid comprises a medical fluid or blood.
 20. Themethod of claim 16, wherein the chamber has an upper surface, and alower surface that runs separate from the upper surface, and whereinmoving along a length of the chamber from the inlet to the outlet of thechamber or from the outlet to the inlet, a distance between the uppersurface and the lower surface changes in at least one dimension of thechamber.
 21. The method of claim 20, wherein the upper surface is in aconcave shape.
 22. A device for measuring conductivity of a fluid, thedevice comprising: a chamber that includes: an inlet, an outlet, whereinthe fluid enters the chamber through the inlet and flows out of thechamber through the outlet, an upper surface, and a lower surface thatruns separate from the upper surface, wherein the upper surface includesmultiple inclined plates such that moving along a length of the chamberfrom the inlet to the outlet or from the outlet to the inlet, a distancebetween the upper surface and the lower surface changes in at least onedimension of the chamber so that bubbles in the fluid are directed froma lower distance region to a higher distance region towards the outletor the inlet; and two electrodes configured to measure electricalvoltage in the fluid that enters the chamber through the inlet and flowsout of the chamber through the outlet.